The ubiquitous growth of wireless communication networks in many areas has the potential to extend wireless data communications far beyond the traditional mobile voice (cellphone) and/or data (smartphone) terminals. As wireless communication network capabilities, capacity, and coverage increase, and as wireless transceiver chip sets and software are more widely and economically available, wireless communications become a viable option for a broad range of systems and devices.
In anticipation of this movement, and to facilitate its implementation, Machine Type Communications (MTC) has been defined as a specific type of wireless communication network traffic. See, e.g., 3GPP Technical Report 23.888, “System Improvements for Machine-Type Communications,” the disclosure of which is incorporated herein by reference in its entirety.
In anticipation of a dramatic proliferation of MTC devices, efforts are underway to mitigate radio interface signaling capacity limitations in existing networks. One aspect of capacity limitation is system access. A brief review of conventional system access signaling follows.
To join a wireless communication network (e.g., to place a voice call, access the internet, or the like), a wireless terminal, such as a cellphone or smartphone, sends an access request message on an access channel. In some protocols, the access request message may be a Channel Request message, and the access channel may be a Random Access Channel (RACH). The access request includes a randomly generated bit sequence which, together with the rest of the information provided within the access request is referred to in some protocols as the Request Reference information. The Request Reference is used for identification purposes during contention resolution and provides some degree of uniqueness for the accessing wireless terminal in lieu of a larger identifier such as the IMSI. The Request Reference thus minimizes the amount of information the wireless terminal must send during the initial part of a contention resolution process. The wireless terminal then monitors a grant channel, such as the Access Grant Channel (AGCH) for a response, for a predetermined monitoring duration, or “window.”
The network may either accept or deny the access request. If it accepts it, the network transmits an explicit access grant response on the grant channel, identifying the wireless terminal by its corresponding random bit sequence (e.g., Request Reference information) and directing it to a traffic channel. In some protocols, the explicit access grant response may be an Immediate Assignment (IA) message. If the network denies access to the requesting wireless terminal, it transmits an explicit access reject response, such as an Immediate Assignment Reject (IAR) message. Current system implementations allow the IAR message to indicate up to four specific wireless terminals that have been rejected, by including the corresponding random bit sequence value for each. As one non-limiting example, access signaling, including IA and IAR messages, is defined for the GSM/EDGE protocols in 3GPP TS 44.018, “Radio Resource Control (RRC) protocol,” the disclosure of which is incorporated herein by reference in its entirety.
If a wireless terminal receives an explicit access reject response within its monitoring window, it waits a first predetermined duration (e.g., starts a “reject” timer) before transmitting another access request message on the access channel. If the wireless terminal receives neither an explicit access grant nor an explicit access reject response within the monitoring window, it waits a second duration (e.g., starts a “no response” timer) before transmitting another access request message on the access channel. To reduce the potential for collisions during subsequent access attempts, at least the second duration may be a randomly generated number, within a predetermined range of values. By imposing these “wait” durations on non-accepted wireless terminals, current systems include some measure of protection against capacity limitations due to a large number of closely spaced system accesses attempted on the access channel.
Conventional wireless communication network access protocols suffer at least two significant deficiencies—inherently limited rejection capacity, and a lack of priority discrimination. As mentioned above, an explicit access reject response (e.g., IAR) can include up to four random bit sequences (e.g., Request References), allowing each such transmission to reject up to four requesting wireless terminals. In a given access window, such as a 1 second time frame, a network node such as a base station may issue approximately thirty explicit access response messages on the grant channel (either access grant or access reject responses). Even in the extreme case that all of the responses are rejections, the network is limited to being able to reject only about 120 requesting wireless terminals during this 1 second time frame. However, in some environments, thousands or even tens of thousands of MTC devices may be requesting network access within a single access window. Hence, for the vast majority of these requests, the network must rely on the predefined “no response” delay to forestall subsequent access requests, since it can only explicitly reject a small fraction of current requests. The conventional “no response” delay (or maximum delay for randomly generated values) is fairly short, as the access request is presumptively associated with real-time user interaction.
The second problem with conventional systems, at least in the face of the MTC device onslaught, is that, since there is no provision for handling different priority requests differently, all requests are de facto high-priority or will at least be treated as having the same priority level. Wireless communication networks were designed, and have evolved, to service real-time user interactions, such as voice calls and interactive data transfers. As a result, the default system values for access delay timers are fairly short, so as not to excessively degrade perceived user experience. Many MTC devices, however, will have relatively low-priority network access needs, in the sense that they can tolerate a significant latency (e.g., many minutes, or even hours) in accessing the network.
Exploitation of this latency tolerance for low-priority network access requests, as well as the ability to reject more than a relative handful of pending requests at a time, may significantly relieve network access traffic congestion caused, or exacerbated, by the proliferation of MTC devices.